As the computer keyboard industry matures, there is an increasing drive among keyboard manufacturers to produce lower cost keyboards. Traditionally, manufacturers have produced a keyboard 10 such as that shown in FIG. 1. One such prior art computer keyboard is disclosed in U.S. Pat. No. 4,560,844 granted to Takamura on Dec. 24, 1985.
Keyboard 10 includes multiple keys 12 mounted in a housing 14, which includes a rigid metal backing plate 16, a rigid metal or plastic mounting plate 18, and a rigid plastic enclosure 20. Keyboard 10 also has a switch membrane 22 and a dome sheet 24 positioned between backing plate 16 and mounting plate 18.
Mounting plate 18 has multiple key supports 26 into which key stems 30 of keys 12 are slidably mounted so that keys 12 can be moved from rest positions to activated positions.
Switch membrane 22 comprises multiple switch contacts positioned beneath respective keys 12. The switch contacts are actuated upon depression of these keys. Dome sheet 24 comprises multiple resilient domes 28 which project upward to bias keys 12 to their rest position. Domes 28 collapse when keys 12 are depressed and rebound to their original form when keys 12 are released by the user to provide the "spring-like" feel of the computer keys. When the keys are depressed, switch membrane 22 conveys an electric signal from the actuated switch contact to an electrical circuit, such as a microprocessor, which is also provided on keyboard 10, but not shown in this figure.
One of the drawbacks of the prior art keyboard shown in FIG. 1 concerns the bearing interface between monoblock key support 26 and key stem 30 of keys 12. At this interface, key stem 30 slides within key support 26, creating surface friction therebetween. As keyboards age, the surface friction increases and keys 12 begin to move less freely. As a result, keyboard users must press harder to depress the computer keys. The necessity of an increased pushing force contributes to user fatigue and other repetitive stress conditions. As the bearing interface further degrades, computer keys often "stick" in the depressed position or return very slowly to the rest position. In such situations, the friction between the key stem 30 and key support 26 is equal to, or greater than, the spring-like force provided by domes 28.
Keyboard manufacturers often lubricate the bearing interface between the key stem and support in an effort to lessen the problems caused by surface friction. Unfortunately, adding such lubricant requires additional assembly time and the use of special lubricants. This contributes to the overall cost of the computer keyboard.
Another drawback of the prior art keyboard shown in FIG. 1 is that individual keys must be separately and independently mounted in their corresponding key supports. Conventional keyboards typically consist of 101 keys. Individually assembling each key requires a significant amount of time and expense.
This invention provides a computer keyboard which eliminates the conventional key stem/support interface and reduces assembly time and expense by decreasing parts count, thereby removing the problems associated therewith.